By 1949, monochrome television had become a commercial success, 10 million
sets had been sold, and programs were available to the general public.
A change to color television would only be licensed if the color broadcast
signal could also be received as a monochrome signal on these sets. This
greatly complicated the technology. RCA was the leading company in the
television field, with CBS a distant second, but CBS advocated the field
sequential color system which utilized rotating disk on which red, green
and blue color filters are mounted. The system was not "compatible" with
the monochrome requirement cited above, but it was practical, especially
under laboratory conditions, and overcame the limitation that the color
television tube, which can integrate three channels of signals (dot sequential),
had not been invented.

CBS was led by William S. Pauley, who was opposed by RCA's David Sarnoff.
CBS executives Frank Stanton and Peter Goldmark, were opposed by RCA's
Elmer Engstrom and George H. Brown. RCA had an technical staff edge, more
development funds, and the virtually unlimited determination of Sarnoff
to make the RCA's dot sequential color system the winner.

The field sequential system (See Figure 1) displayed red, green, and
blue television images in sequences, and depended upon the retentivity
of the eye to merge these into a single color picture. If, however, flicker
and picture sharpness were to be maintained at the level of monochrome
television, a field sequential broadcast signal would require three times
the bandwidth of monochrome. A compromise or trade off was reached by increasing
the bandwidth from 4 to 5 MHz, number of frames were reduced from 30 to
20 per second, and scanning lines reduced from 525 to 343. RCA labeled
this system as "mechanical", which was true of the color tube system only.

RCA's dot sequential system approach to solve the bandwidth limitation
(see Figure 2), was one proposed by Alda Bedford of RCA, the use of "mixed
highs." This relied on the limitation of the eye's relative insensitivity
to the fine detail of color, the portion of the picture that requires the
transmission of higher frequency components. Bedford proposed that these
components be separated from the three color signals, mixed, and then added
to the GREEN signal. The bandwidth of the red and blue signals could then
be reduced substantially. Another addition, the use of a burst (train of
8 cycles of a sine wave) to the color signal provided a solid synchronism
between camera source and receiver, and overcame noise which would cause
instability. Field tests brought about the change of color to orange-red
and blue-green to take advantage of the eye's insensitivity to fine detail
in the blue-green region, thereby narrowing the blue-green band.

CBS won approval of its field sequential system and started expensive
color broadcasts. However, the sets did not sell and had no audience. CBS
was able to gracefully back-out by the intervention of the Korean War,
and the ban on strategic material.

The basic operation of the field sequential color system is shown
above. Light from the scene passes through a rotating disk on which red,
green and blue color filters are mounted. Thus a camera tube is exposed
in sequence to the red, green and blue color components of the scene. A
disk at the receiver, similarly equipped with color filters, rotates in
synchronism so that the light from the kinescope passes through the red
filter, for example, while the camera tube is being exposed to red light
from the scene.

The bottom portion of Figure 1 shows the color sequence in successive
fields of the color signal as proposed by CBS in the 1949 hearing. Note
that only two colors are included in each frame; for example, frame 1 has
red odd lines and green even lines. Six fields, or 1/8 second, was required
to scan all lines in all three colors. This caused fast-moving white objects
to exhibit color break-up -- that is, to appear as a series of colored
objects.

Figure 2

Principle of the dot sequential system.

Red, green and blue color signals are produced continuously and simultaneously.
These signals are then sampled in sequence at a rapid rate, nominally 3.6
MHz. The output of the sampling process is a series of pulses, each having
an amplitude proportional to the amplitude of the corresponding color signal
at that point in the picture. This signal produces a series of tiny (approximately
0.03" wide) colored dots on a tricolor kinescope. These are perceived by
the eye as a single color with a hue determined by the relative amplitude
of the red, green and blue pulses at that point.